Magnetic disk drives are conventionally designed to store large volumes of data on a plurality of disks mounted on a spindle assembly. Typically, each disk includes two disk surfaces capable of storing data. On each disk surface, user data is divided into groups of sectors and stored in concentric circular tracks located between an outside diameter and an inside diameter of the disk. Embedded servo information is recorded in servo sectors located in radially continuous narrow wedges along the disk surface.
In order to maximize the data recorded on each disk surface, it is often desirable to use zone banding for both data and servo sectors. In zone banding, the rate or frequency at which data/servo information is recorded to a disk surface increases from the inner tracks to the outer tracks to compensate for the fact that tracks toward the inside diameter of the disk surface are shorter and can hold less data/servo information than tracks near the outside diameter. Thus, using zone banding, relatively uniform data and servo densities may be achieved over the entire disk surface.
Although frequencies could theoretically be optimized for each track, zone banding techniques typically utilize a relatively low number of discrete data and servo frequencies. Accordingly, groups of adjacent tracks may be assigned to an array of zones between the innermost and the outermost track of a disk surface. For example, there may be between five and 20 data zones across a disk surface, and between three and ten servo zones across the disk surface. Data may be written at the same recording frequency within each data zone, and the recording frequency may increase from the inner data zones to the outer data zones. Similarly, servo sectors may be recorded at the same servo frequency within each servo zone, and the servo frequency may increase from the inner servo zones to the outer servo zones.
Unfortunately, disk drive performance may be adversely impacted when crossing servo zone boundaries. For example, a conventional disk drive generates a number of system clocks based on the current servo frequency and may require a particular set of filtering and demodulation parameters when reading servo information at the current servo frequency. When the disk drive begins reading from a new servo zone, these system clocks and filtering and demodulation parameters will be at least momentarily out of synchronization with the new servo frequency. Typically, the process of synchronization with the new servo zone takes a relatively long time (e.g., >3 servo wedges), during which the disk drive is unable to optimally seek, track follow, or read/write data.
There is therefore a need in the art to improve the implementation of zoned servo in disk drives.